The present invention relates to improved set retarders for foamed cements, foamed cement compositions containing the improved set retarders, and to improved methods of cementing in subterranean zones with set retarded foamed cement compositions.
Foamed hydraulic cement compositions are often utilized in cementing subterranean zones penetrated by well bores. For example, foamed cement compositions are used in primary well cementing operations whereby strings of pipe such as casing and liners are cemented in well bores. In performing primary cementing, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. Examples of foamed hydraulic cement compositions are described in U.S. Pat. No. 5,897,699 and U.S. Pat. No. 6,063,738.
The cement compositions utilized for cementing in subterranean zones or formations penetrated by well bores must often be lightweight to prevent excessive hydrostatic pressure from unintentionally fracturing the zones or formations. In addition to being lightweight, a foamed cement composition contains compressed gas which improves the ability of the cement composition to maintain pressure and prevent the flow of formation fluid into and through the cement composition during the transition time, i.e., the time during which the cement composition changes from a true fluid to a hard set mass. Foamed cement compositions are also advantageous because they have low fluid loss properties.
When cement compositions are utilized for cementing in deep hot subterranean zones, a set retarder must be included in the cement composition to increase the pumping time of the composition and prevent premature thickening or setting before placement in the zones to be cemented. Examples of set retarders which have heretofore been utilized in non-foamed cement compositions include, but are not limited to, lignosulfonates, sulfomethylated lignosulfonates, hydroxycarboxy acids, mixtures of sulfomethylated lignosulfonates and hydroxycarboxy acids, acrylic acid/2-acrylamide-2-methyl propane sulfonic acid copolymers and the like. While the foregoing set retarders function well in non-foamed cement compositions, they do not function well in foamed cement compositions because they have dispersing properties. That is, when used in a foamed cement composition, a set retarder having dispersing properties causes the cement slurry to be thin which in turn causes the foam to be unstable and either break or significantly decrease the viscosity of the foamed cement slurry which in turn prevents the desired foamed cement composition low density from being achieved. While carboxymethylhydroxyethylcellulose (CMHEC) has heretofore been used in foamed cement compositions as a set retarder, the high concentrations of CMHBC required causes the foamed compositions to have undesirable high surface viscosities.
Thus, there are needs for improved methods, set retarding additives, and set retarded foamed cement compositions for cementing subterranean zones penetrated by well bores.
The present invention provides improved set retarders for foamed cement systems, and cement compositions formed therewith. The set retarders comprise a blend of a sulfonated lignin functioning as a set retarder and an alkali lignin containing 0-3.5% organic sulfur functioning as a stabilizer. The sulfonated lignin may be either a lignosulfonate (sulfite lignin), or a sulfonated alkali lignin with an organic sulfur content of about 2% or greater. The sulfonated lignin may be used xe2x80x9cas-isxe2x80x9d or in a further modified form so long as the organic sulfur content is about 2% or greater, preferably 5% or greater and most preferably 2-12%. The stabilizing alkali lignin may be an unsulfonated kraft lignin or a kraft lignin with a low organic sulfur content, i.e., 3.5% or less. The set retarder and stabilizer ingredients may be blended in a ratio of about 6:4 to about 8:2, and blending may be accomplished by dry blending or by mixing solutions of the two components together and spray drying.
The present invention also provides improved methods for cementing in subterranean zones penetrated by well bores which meet the needs described above and overcome the deficiencies of the prior art. The improved methods of this invention are basically comprised of the following steps. A foamed cement composition is prepared comprised of hydraulic cement, a non-dispersing set retarder comprised of a mixture of a sulfonated lignin containing at least 2% organic sulfur and an alkali lignin containing 0-3.5% organic sulfur, sufficient water to form a slurry, sufficient gas to foam the slurry and a foaming and foam stabilizing surfactant mixture. The foamed cement composition is then placed into a subterranean zone, and the foamed cement composition is allowed to set into a solid mass therein.
It is, therefore, a general object of the present invention to provide improved methods of cementing in subterranean zones penetrated by well bores.
Another object is to provide improved set retarder additives for foamed cements, as well as to provide improved cement compositions incorporating such set retarders for use in the completion and remediation of subterranean wells.
A further object of the present invention is to provide improved methods of cementing in subterranean zones penetrated by well bores with a foamed cement slurry containing a non-dispersing set retarder.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
The improved methods, additives, and foamed cement compositions of the present invention are particularly suitable for performing a variety of completion and remedial procedures in subterranean zones or formations penetrated by well bores. The foamed cement compositions have improved properties in that they include a non-dispersing set retarder additive which does not cause the foamed cement compositions to break or decrease in viscosity whereby the density of the foamed cement compositions increases. Since it is often very important that the density of a foamed cement composition be as low as possible, an increase in density can cause adverse cementing results, e.g., fracturing of the formation or zone being cemented.
The foamed cement compositions useful in accordance with this invention are basically comprised of a hydraulic cement, a non-dispersing set retarder comprised of a sulfonated lignin containing at least about 2% organic sulfur and an alkali lignin containing 0% to about 3.5% organic sulfur, sufficient water to form a slurry, sufficient gas to foam the slurry and a surfactant present in an amount sufficient to facilitate the formation of the foam and stabilize the foamed cement composition.
A variety of hydraulic cements can be utilized in accordance with the present invention including those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, pozzolana cements, gypsum cements, high alumina content cements, silica cements and high alkalinity cements. Portland cements or their equivalents are generally preferred for use in accordance with the present invention when performing cementing operations in subterranean zones penetrated by well bores. Portland cements of the types defined and described in API Specification For Materials And Testing For Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred API Portland cements include classes A, B, C, G and H, with API classes G and H being more preferred, and class G being the most preferred.
As used herein, the term xe2x80x9calkali ligninxe2x80x9d refers to the class of lignin that is derived from the kraft and soda pulping processes, and is recovered as a precipitate from the pulping liquors of the pulp industry where lignocellulosic materials, such as wood, straw, corn stalks, bagasse and the like, are processed to separate the cellulose pulp from the lignin by treating said materials with caustic and/or sulfide. Alkali lignin is not a sulfonated product, and thus is water-insoluble at acidic pH. However, it can be readily modified, if desired, by reacting with a sulfite compound or a carboxylating agent, or by oxidizing with common oxidants of lignin such as O2, O3 and H2O2, or any combination of these reactions, to improve water solubility. The most common alkali lignin is the kraft lignin (or sulfate lignin) produced in the pulping of wood by the kraft process.
The term xe2x80x9csulfite ligninxe2x80x9d refers to the lignin material conventionally and inherently obtained in the sulfite pulping of wood and other lignocellulosic materials. Sulfite lignin is inherently obtained as a sulfonated product, and is readily soluble in water. It is also called xe2x80x9clignosulfonate,xe2x80x9d and is the principal constituent of spent sulfite liquor. It also refers to the spent sulfite liquor solids which contain, besides lignin as the principal constituent, wood sugars and other organic compounds.
The term xe2x80x9csulfonated lignin,xe2x80x9d as used herein, encompasses not only the sulfite lignin (or lignosulfonate) but also xe2x80x9csulfonated alkali ligninxe2x80x9d which refers to the product obtained by the introduction of sulfonic acid groups into the alkali lignin molecule, as may be accomplished by reaction of a kraft lignin with sulfite or bisulfite compounds, so that the kraft lignin is rendered soluble in water.
Sulfonated lignin is used as the set retarder ingredient in the improved additive of the present invention. Sulfonated lignin, both of hardwood and softwood origin, may be utilized herein in the xe2x80x9cas-isxe2x80x9d or whole liquor condition, or in a purified form, partially or fully devoid of sugars as noted previously herein, or additionally of inorganic constituents such as sodium chloride, sodium sulfate, sodium sulfite, and various other ionic species or salts. In addition, lignosulfonates in various salt-forms including sodium lignosulfonates, calcium lignosulfonates, sodium/calcium lignosulfonates, ammonium lignosulfonates, potassium lignosulfonates, magnesium lignosulfonates, potassium/calcium lignosulfonates, and mixtures or blends thereof may also be utilized herein. Preferably, lignosulfonates in their xe2x80x9cas-isxe2x80x9d or whole liquor condition are employed. The specific lignosulfonate that is preferred for use as the set retarder ingredient of this invention is a hardwood lignosulfonate liquor having a sulfur content of about 6% by weight and an average molecular weight of about 9,700 daltons. The one or more sugar acids in the liquor are preferably derived from xylose. Lignosulfonates are available from numerous sources in either aqueous solution or dried powder forms. For example, Lignotech USA, Inc., sells lignosulfonates under the trade designations Lignosol, Norlig, and Marasperse which are appropriate for use in the present invention.
The sulfonated lignin used as the set retarder ingredient of the present additive may also be a sulfonated alkali lignin with an organic sulfur content of about 2% or greater. As noted previously, alkali lignin is a non-sulfonated product derived from the kraft and/or soda pulping processes, and is thus insoluble in water at acidic pH. However, alkali lignin may be sulfonated by the introduction of sulfonic acid groups into the kraft lignin molecule, as may be accomplished by reaction of the kraft lignin with sulfite or bisulfite compounds via known techniques and processes, so that kraft lignin is rendered soluble in water. To be useful as the set retarder ingredient in the present additive, the alkali lignin should be sulfonated to a degree such that it contains at least about 2% or greater organic sulfur, and preferably 3.5% to 7.0%.
Modified sulfonated lignin may also be used as the set retarder ingredient in the additive. By xe2x80x9cmodified,xe2x80x9d it is meant sulfonated liquor that is further reacted, purified, fractionated, and the like. Specifically, modified sulfonated lignin includes desugared products (e.g., by fermentation or chemical reaction), ammoxidized products (e.g. oxidation with ammonia or an amine), carboxylated products (e.g. by air, hydrogen peroxide or ozone oxidation), graft copolymerized products (e.g. with acrylic monomers such as acrylic acid), desulfonated products (e.g. by high temperature, high pressure oxidation), and purified products (e.g. by ultrafiltration). All of the above modified sulfonated lignins may be obtained via known techniques and processes.
Specifically modified lignosulfonates of use in the present invention are those which have been ammoxidized, i.e. reacted with ammonia or an amine in the presence of an oxidant. Lignosulfonates to be used in making ammoxidized products may be obtained from any number of commercial sources. Some typical lignosulfonates that may be used in this reaction include: sodium lignosulfonate such as Lignosol SFX-65 and Borresperse NA (manufactured by Borregaard LignoTech); calcium lignosulfonate such as Lignosite 50 (manufactured by Georgia Pacific); sodium/calcium lignosulfonate such as Norlig 24C; ultrafiltered sodium and calcium lignosulfonates such as Ultrazine NA and Ultrazine CA (all manufactured by Borregaard LignoTech), respectively.
Generally, the ammoxidation reaction is carried out by dissolving the lignosulfonate in water to a solids level of 10 to 60%, more preferably to a level of 30%, adjusting the pH to 6-10, adding the desired amine and oxidant, and heating for 0.25 to 20 hours at 90-180 C. The reaction is most easily carried out in a pressure reactor. Sulfonated lignin used for this process may be obtained either from lignosulfonate or from sulfonation of Kraft or organosolve lignin.
Oxidizing agents such as oxygen, air, hydrogen peroxide, ozone are considered as acceptable oxidants. The amines that may be reacted with lignosulfonate include ammonia, and other primary and secondary alkyl amines such as pentaethylenehexamine, hexamethyleneamine and the like. In particular, organic amines that may be reacted with lignosulfonate are primary amines such as methylamine, ethylamine, ethylenediamine, benzylamine or aniline, secondary amines such as dimethylamine, diethylamine, diisobutylamine, methylphenylamine and ethylbenzylamine, and tertiary amines like trimethylamine, triethylamine or tributylamine. The amount of oxidant used is between 0.01 to 2 moles per 100 g of lignosulfonate, more preferably between 0.15 to 0.25 moles per 100 g of lignosulfonate. The lignosulfonate or the sulfonated lignin can be treated with oxidizing agents such as hydrogen peroxide and the like prior to ammoxidation. A set of typical reaction conditions for ammoxidation includes 28% lignin solids by weight of the reaction mixture, 3% ammonia by weight of the lignin, 3-6% hydrogen peroxide by weight of the lignin, heating at 165xc2x0 C under 200 psi of oxygen or air pressure for 1 hour.
The preferred xe2x80x9cde-sugaredxe2x80x9d sulfonated lignin is an ultrafiltered lignosulfonate. The term xe2x80x9cde-sugaredxe2x80x9d is meant to encompass sulfonated lignin products containing 2% or less of sugars, and preferably 1% or less of sugars. The method of calculating the percentage of sugar is determined by the reducing sugars method practiced in the industry (Brown, C. A., and Zerban, F. W. xe2x80x9cSugar Analysis,xe2x80x9d 3rd Edition, John Wiley and Sons, Inc., 1941). The term xe2x80x9csugarsxe2x80x9d is meant to include any of various water-soluble carbohydrates normally referred to as sugars in this industry and typically contained in lignosulfonates, including but not limited to saccharides such as mono- or di-saccharide sugars like sucrose, manose, arabinose, rhamnose, galactose, glucose and xylose, as well as polymerized sugars or sugar acids such as gluconic acid and mono- or di-carboxylic acid decomposition products of the above sugars.
An alkali lignin containing 0% to about 3.5% organic sulfur is used as the foam stabilizer ingredient in the improved additive of the present invention. To be useful, the alkali lignin must contain either no sulfonation or a low degree of sulfonation. The preferred alkali lignin is a kraft lignin, i.e. a lignin obtained from the kraft process, and is a kraft lignin having an average molecular weight of about 60,000 daltons. Examples of alkali lignin suitable for use as the foam stabilizer ingredient of the additive include xe2x80x9cCuron 27-11P,xe2x80x9d a kraft lignin with about 2% organic sulfur available from LignoTech USA, Inc., xe2x80x9cIndulin AT,xe2x80x9d a kraft lignin with about 2% organic sulfur available from Westvaco, and xe2x80x9cDiWatex XP-9,xe2x80x9d a sulfonated kraft lignin with about 3.5% organic sulfur available from LignoTech USA, Inc.
The non-dispersing set retarder is preferably comprised of a mixture of about 59 parts by weight lignosulfonate, about 11 parts by weight sugar acid and about 30 parts by weight kraft lignin. As will be understood by those skilled in the art, the amount of the non-dispersing set retarder included in the foamed cement compositions of this invention can vary depending upon the particular pumping time required. Generally, the non-dispersing set retarder is present in a foamed cement composition of this invention in an amount in the range of from about 0.05% to about 3.0% by weight of hydraulic cement in the composition, preferably from about 0.05% to about 2.75% by weight, and most preferably from about 0.1% to about 2.75% by weight. The set retarder ingredient is blended with the foam stabilizer ingredient in a ratio of about 1:1 to 4:1, preferably about 6:4 to 8:2, and most preferably in a ratio of about 7:3.
The water utilized to form the foamed cement compositions of this invention can be fresh water or salt water. The term xe2x80x9csalt waterxe2x80x9d is used herein to mean unsaturated salt solutions and saturated salt solutions including brines and seawater. The water is included in the foamed cement compositions in an amount sufficient to slurry the hydraulic cement. Generally, the water is present in the foamed cement compositions in an amount in the range of from about 30% to about 60% by weight of hydraulic cement.
The gas utilized for foaming the cement slurry can be air or nitrogen, with nitrogen being preferred. The gas is present in an amount sufficient to foam the slurry, generally in an amount in the range of from about 5% to about 60% by volume of the slurry.
A variety of foaming and foam stabilizing surfactants can be utilized in accordance with the present invention. Examples of suitable surfactants include surfactants having the general formula H(CH2)a(OC2H4)bOSO3X wherein a is an integer in the range of from about 5 to about 15; b is an integer in the range of from about 1 to about 10; and X is any compatible cation. A particularly preferred foaming agent is a surfactant of the above type having the formula H(CH2)a(OC2H4)3OSO3Na wherein a is an integer in the range of from about 6 to about 10. This surfactant is commercially available from Halliburton Energy Services of Duncan, Oklahoma, under the trade designation xe2x80x9cCFA-STM(trademark).xe2x80x9d
Another particularly preferred foaming agent of the above mentioned type is a surfactant having the formula H(CH2)a(OC2H4)bOSO3NH4 wherein a is an integer in the range of from about 5 to about 15; and b is an integer in the range of from about 1 to about 10. This surfactant is available from Halliburton Energy Services under the trade name xe2x80x9cHALLIBURTON FOAM ADDITIVE(trademark).xe2x80x9d
Yet another surfactant is a sodium salt having the formula R7(OR8)pSO3X wherein R7 is an alkyl group having in the range of from about 5 to about 20 carbon atoms, R8 is the group xe2x80x94CH2CH2xe2x80x94, p is an integer in the range of from about 10 to about 40 and X is a compatible cation. A particularly preferred surfactant of this type is the sodium salt of a sulfonated compound derived by reacting a C12 to C15 alcohol with about 15 moles of ethylene oxide having the formula H(CH2)12-15(CH2CH2O)15SO3Na which is commercially available under the name xe2x80x9cAVANEL S150(trademark)xe2x80x9d from PPG Mazer, Mazer Chemicals, a Division of PPG Industries, Inc., 3938 Porett Drive, Gurnee, Ill. 60031. Of the various stabilizers described above which can be used, ethoxylated nonylphenol containing in the range of from about 15 to about 40 moles of ethylene oxide and the xe2x80x9cAVANEL(trademark)xe2x80x9d series of surfactants, i.e. the sodium salt of a sulfonated and ethoxylated compound having the formula H(CH2)12-15(CH2CH2O)15-40SO3Na are preferred.
A preferred mixture of such surfactants is described in U.S. Pat. No. No. 5,897,699 issued to Chatterji et al. on Apr. 27, 1999 which is incorporated herein by reference. The patent discloses an aqueous solution of a mixture of an alpha-olefinic sulfonate and a cocoylamidopropyl betaine.
A particularly preferred foaming and foam stabilizing surfactant mixture for use in accordance with the present invention is comprised of an ethoxylated alcohol ether sulfate of the formula H(CH2)a(OC2H4)bOSO3NH4+ wherein a is an integer in the range of from about 6 to about 10 and b is an integer in the range of from about 3 to about 10, an alkyl or alkene amidopropylbetaine having the formula Rxe2x80x94CONHCH2CH2CH2N+(CH3)2CH2CO2 wherein R is a radical selected from the group of decyl, cocoyl, lauryl, cetyl and oleyl, and an alkyl or alkene amidopropyldimethylaminoxide having the formula Rxe2x80x94CONHCH2CH2CH2N+(CH3)2O wherein R is a radical selected from the group of decyl, cocoyl, lauryl, cetyl and oleyl.
The ethoxylated alcohol ether sulfate is generally present in the above-described mixture in an amount in the range of from about 60 to 64 parts by weight. The alkyl or alkene amidopropylbetaine is generally present in the mixture in an amount in the range of from about 30 to about 33 parts by weight and the alkyl or alkene amidopropyldimethylamineoxide is generally present in the additive in an amount in the range of from about 3 to about 10 parts by weight. In order to make the surfactant mixture more easily combinable with the cement slurry, water can be combined with the mixture in an amount sufficient to dissolve the surfactants.
The most preferred foaming and foam stabilizing surfactant mixture of the type described above for use in accordance with this invention is comprised of an ethoxylated alcohol ether sulfate wherein xe2x80x9caxe2x80x9d in the formula set forth above is an integer in the range of from 6 to 10 and the ethoxylated alcohol ether sulfate is present in the surfactant mixture in an amount of about 63.3 parts by weight; the alkyl or alkene amidopropylbetaine is cocoylamidopropylbetaine and is present in the mixture in an amount of about 31.7 parts by weight, and the alkyl or alkene amidopropyldimethylamineoxide is cocoylamidopropyldimethylamineoxide and is present in an amount of about 5 parts by weight.
The foaming and foam stabilizing surfactant is generally included in the foamed cement composition of this invention in an amount in the range of from about 1% to about 5% by volume of water in the cement slurry, preferably in an amount of from about 1% to about 2.5%.
A particularly preferred foamed cement composition for use in accordance with this invention is comprised of Portland cement, a non-dispersing set retarder comprised of a mixture of about 59 parts by weight hardwood lignosulfonate, about 11 parts by weight xylose sugar acid and about 30 parts by weight sulfonated kraft lignin, sufficient water to form a slurry, sufficient nitrogen to foam the slurry and a foaming and foam stabilizing surfactant mixture present in an amount sufficient to facilitate the formation of the foam and stabilize the foamed cement composition.
The non-dispersing set retarder is preferably included in the above-described foamed cement composition in an amount in the range of from about 0.05% to about 3% by weight of hydraulic cement therein. The water used is preferably included in the composition in an amount in the range of from about 30% to about 60% by weight of hydraulic cement therein, and the nitrogen is preferably present in the composition in an amount in the range of from about 5% to about 60% by volume of the composition. The foaming and foam stabilizing surfactant mixture is preferably comprised of an ethoxylated alcohol ether sulfate present in an amount of about 63.3 parts by weight of the mixture, cocoylamidopropylbetaine present in an amount of about 31.7 parts by weight of the mixture and cocoylamidopropylbetaine present in an amount of about 5 parts by weight of the mixture. The foaming and foam stabilizing surfactant mixture is preferably present in the foamed cement composition in an amount in the range of from about 1% to about 2.5% by weight of water therein.
A preferred method of the present invention for cementing in a subterranean zone penetrated by a well bore is comprised of: (a) preparing a foamed cement composition comprised of Portland cement, a non-dispersing set retarder comprised of a mixture of 59 parts by weight hardwood lignosulfonate, 11 parts by weight xylose sugar acid and 30 parts by weight sulfonated kraft lignin present in an amount in the range of from about 0.05% to about 3.0% by weight of hydraulic cement in the composition, sufficient water to form a slurry, sufficient nitrogen to foam the slurry, and a foaming and foam stabilizing surfactant mixture comprised of an ethoxylated alcohol ether sulfate present in an amount of about 63.3 parts by weight of the mixture, cocoylamidopropylbetaine present in an amount of about 31.7 parts by weight of the mixture and cocoylamidopropyldimethylamineoxide present in an amount of about 5 parts by weight of the mixture, the foaming and foam stabilizing surfactant mixture being present in the composition in an amount in the range of from about 1% to about 2.5% by weight of water therein; (b) placing the foamed cement composition into the subterranean zone; and (c) allowing the foamed cement composition to set into a solid mass therein.
U.S. patent application Ser. No. 09/569,519, entitled xe2x80x9cMethods of Cementing Subterranean Zonesxe2x80x9d filed on even date herewith i.e. May 12, 2000 now U.S. Pat. No. 6,227,294, which describes and claims methods of cementing using similar non-dispersing set retarders and foamed cement compositions is incorporated herein in its entirety by reference.